Uterus-like mass involving the appendix: US and CT findings

Uterus-like mass is a rare extrauterine mass composed of a central cavity lined by endometrium and surrounding smooth muscle. Uterus-like mass has frequently been reported in the ovary, but has rarely been found in extraovarian regions. We report a case of uterus-like mass involving the appendix in a woman who presented with right lower abdominal pain indistinguishable from acute appendicitis. Sonography revealed a heterogeneous mass of mixed echogenicity with inner cystic change, abutting the appendix. CT depicted an enhanced mass with inner cystic change abutting the appendix. Histopathologic examination confirmed the diagnosis.